Who wrote the United States Constitution?

James Madison is often referred to as the "Father of the Constitution" due to his pivotal role in its drafting and his influential contributions to the Constitutional Convention of 1787. He played a crucial part in the discussions and debates that shaped the structure and principles of the Constitution. Madison's extensive notes from the convention provide valuable insights into the framers' intentions and the challenges they faced. While he was supported by key figures such as George Washington, who presided over the convention, and Alexander Hamilton, who advocated for a strong central government, Madison's intellectual leadership and commitment to democratic principles were fundamental to the creation of the Constitution.

Thomas Jefferson, although an important Founding Father and the author of the Declaration of Independence, was not directly involved in the drafting of the Constitution, as he was serving as the ambassador to France during the convention. Therefore, Madison's significant role in writing and promoting the Constitution makes him the correct answer to the question.